The light-emitting diode (LED) is a solid state semiconductor device, which has been broadly used as a light-emitting device. The light-emitting device comprises a p-type semiconductor layer, an n-type semiconductor layer and an active layer. The active layer is formed between the p-type semiconductor layer and the n-type semiconductor layer. The light-emitting device generally comprises III-V group compound semiconductor such as gallium phosphide, gallium arsenide, or gallium nitride. The light-emitting principle of the LED is the transformation of electrical energy to optical energy by applying electrical current to the p-n junction to generate electrons and holes. Then, the LED emits light when the electrons and the holes combine.
When the LED is used for display apparatus or the like, typical usage conditions are approximately 1 V to 4 V for the drive voltage and approximately 20 mA for the drive current. With the recent development of the short-wavelength LEDs which uses a GaN-based compound semiconductor and commercialization of solid light sources of full color, white color, etc., application of the LEDs for illumination purposes has been considered. When the LED is used for illumination, there may be cases in which the LED is used under conditions other than the above-described conditions of 1 V-4 V of drive voltage and 20 mA of drive current. As a result, steps have been taken to enable a larger current to flow through the LED and to increase the light emission output. Generally, because of the requirements of light intensity and light efficiency of the LED, a high voltage LED is formed by electrically connecting two or more light-emitting elements.
During the fabrication processes of the high voltage LED, some manufacture deviations such as incoming materials, equipment malfunction or process excursion may happened, and that cause one or more light-emitting elements of the high voltage LED having different electrical bins.
FIG. 1 illustrates a conventional high voltage light-emitting device 1. The high voltage light-emitting device 1 comprises a plurality of light-emitting elements 10, 12, and 14 electrically connected with each other through a connection structure 11. As shown in FIG. 1, the high voltage light-emitting device 1 comprises fifteen light-emitting elements arranged in three columns 1a, 1b, and 1c. The first column 1a comprises one light-emitting element 10 and four light-emitting elements 12 connected in series in a first direction. The second column 1b comprises five light-emitting elements 12 connected in series in a second direction. The third column 1c comprises one light-emitting element 14 and four light-emitting elements 12 connected in series in the first direction. The first direction and the second direction are opposite. Each of the plurality of light-emitting elements 10, 12, and 14 comprises a semiconductor stack comprising an n-type semiconductor layer, a p-type semiconductor layer, and an active layer formed between the n-type semiconductor layer and the p-type semiconductor layer. The high voltage light-emitting device 1 further comprises a first electrode 100 formed on the light-emitting element 10 and a second electrode 140 formed on the light-emitting element 14. The first electrode 100 and the second electrode 140 are formed for wire bonding or flip chip type bonding. The polarities of the first electrode 100 and the second electrode 140 are different from each other. During the electrical test, the first electrode 100 and the second electrode 140 can correspond to a pair of external electrodes (not shown) such as probes. As shown in FIG. 1, the high voltage light-emitting device 1 further comprises an electrical finger structure 10a formed on the light-emitting element 10, an electrical finger structure 14a formed on the light-emitting element 14, and an electrical finger structure 12a formed on each of the plurality of light-emitting elements 12. The number of the light-emitting elements 12 formed between the light-emitting element 10 and the light-emitting element 14 is increased based on the desired quantity of light of the high voltage light-emitting device 1.
During the electrical test, a current from the probes is injected into the high voltage light-emitting device 1 through the first electrode 100 and the second electrode 140. The current injected from the first electrode 100 and the second electrode 140 spreads out in the light-emitting element 10 and the light-emitting element 14 through the electrical finger structures 10a and 14a respectively. The current further spreads between the plurality of light-emitting elements 12 via the electrical finger structure 12a and the connection structure 11.
In the conventional electrical test, a pair of probes contacts the first electrode 100 and the second electrode 140 correspondingly to test the electrical yield and electrical properties of the high voltage light-emitting device 1. The electrical properties can be reverse leakage current and forward voltage. Nevertheless, the conventional electrical test measurement can only get the overall electrical yield and electrical properties of the high voltage light-emitting device 1, and the electrical properties of each of the plurality of light-emitting elements 10, 12, and 14 are difficult to identify. If there is an electrical defect in one of the plurality of light-emitting elements 10, 12, and 14 during the fabrication processes, the electrical defect may degrade the reliability of the high voltage light-emitting device 1.